Distribution characteristics and influence factors of the ammonia, nitrite and nitrate in the Lijiang River, Guilin City

The Lijiang River, an internationally famous karst scenic area, is the main source for massive water supply to Guilin City. It is reported that ammonia is one of three major nitrogenous contaminants, according to the monitoring data derived from 962 water stream sections in ten first catchments across China. To determine the temporal and spatial distribution characteristics of ammonia-nitrite-nitrate and associated influential factors, 7 sections on the Lijiang River and its tributaries are selected. The samples of surface water were collected during the wet and dry seasons, respectively. The analytical results of field chemical/physical parameters and laboratory experiments show that the highest concentrations of NH3-N and NO3--N are 0.248 3 mg/L and 2.251 7 mg/L, respectively, which fall in the range of gradeⅡwater recommended by the national environmental surface water quality standards. The concentration of NO3--N is also below the limit requirement of surface water sources for collective drinking water supply. However, the results also show that the ammonia-nitrite-nitrate concentrations in the Lijiang River have increased by various degrees and the water has a tendency of deterioration after the river flows through the Guilin City. The temporal distribution characteristics of ammonia-nitrite-nitrate is that the concentrations of NH3-N and NO3--N are higher during dry seasons and the concentration of NO2--N becomes higher during wet seasons, The ratio of C(NH3-N)/ C(TIN) is 4.83% in wet seasons; and the figure rises to 6.69% in dry seasons because of temperature change. The increasing of ammonia nitrite and nitrate nitrogen is attributed to the additional pollutants contributed from the tributaries of the river such as Xiaodongjiang river and Taohuajiang river, which are flowing through the rural domestic and agricultural area where is lack of sanitation facilities. In addition, the concentration of NH3-N has a raising trend and the concentration of NO2--N and NO3--N is almost steady when it rains or during flood seasons because of agricultural non-point sources. Therefore, it is necessary to control and manage the contaminant inflow from the tributaries of the Lijiang River in a comprehensive manner and develop a real-time network to monitor the water sources area, especially monitor the NH3-N concentration fluctuation in rainy season.